For the chuck mechanism of a machine tool such as a lathe or so (for example see Patent document 1), in order to carry out a highly precise processing to the workpiece, a centering of workpiece needs to be done with high precision, and/or when the workpiece is removed and installing it again, the centering of the workpiece needs to be done accurately even in case of repeating. As the chuck which can correspond to such demand, a chuck mechanism has been proposed such that plurality of serrations are formed which extend in different directions of the face contacting with a master jaw, and by engaging these, the soft jaw prevents the shifting in the plane direction of the contacting face between the master jaw (for example, see Patent document 2).